Pyongyang calls sanctions and pressure 'futile' in halting its development of nuclear weapons.

North Korea's state news agency has called the US-led effort to impose sanctions over its weapons programme futile, vowing the country inevitably will become a "state nuclear force".

The comments on Sunday came from the Korean Central News Agency's website Uriminzokkiri after US Secretary of State Rex Tillerson met for talks with China's top diplomats and President Xi Jinping in Beijing over the Korean nuclear crisis.

Tillerson has been a proponent of a campaign of "peaceful pressure", using US and UN sanctions and working with China to turn the screw on the regime.

But his efforts have been overshadowed by an extraordinary war of words, with US President Donald Trump mocking North Korean leader Kim Jong-un as "little rocket man" and Kim branding Trump a "dotard".

"The US and the South Korean puppet forces are mistaken if they think that sanctions and pressure will keep the DPRK from attaining the goal of completing the state nuclear force," said KCNA, using the acronym for the country's official name, Democratic People's Republic of Korea.

"The US and vassal forces would be well advised to bear in mind that their frantic sanctions - contrary to the trend of the times - will lead to their final doom."

Washington has reached out to Pyongyang but received no response.

"We ask: Would you like talk?" Tillerson said on Saturday. "We're not in a dark situation, a blackout. We have a couple, three channels open to Pyongyang."

In Washington, the State Department said while communications channels do exist, North Korea has shown no interest in talking about giving up its nuclear weapons.

"Despite assurances that the United States is not interested in promoting the collapse of the current regime, pursuing regime change, accelerating reunification of the peninsula or mobilising forces north of the DMZ [de-militarised zone], North Korean officials have shown no indication that they are interested in or are ready for talks regarding de-nuclearisation," spokeswoman Heather Nauert said in a statement.

The United States has not ruled out the use of force to compel Pyongyang to halt missile and nuclear tests, and last week Trump threatened to "totally destroy" the country.

But privately senior figures admit military options don't look promising, with ally South Korea's densely populated capital Seoul - a city of 25 million people - in range of the North's heavy artillery.

Even as Tillerson met Xi and China's top diplomats State Councillor Yang Jiechi and Foreign Minister Wang Yi, the North's propaganda agency fired a new barrage of insults.

A statement proclaimed Trump an "old psychopath" bent on the "suicidal act of inviting a nuclear disaster that will reduce America to a sea of flames".